Bourdon tube



y 1929. H. SCHLAICH 1. 14.988

BOURDON TUBE Filed July 15, 1924 Patented May 28, 1929.

UNITED STATES HERMAN SCHLAICH, OF LONG ISLAND CITY, NEW YORK.

BOURDON TUBE.

Application filed July 15,

This present invention relates to pressure responsive instruments, andmore particularly to a Bourdon tube.

Certain instruments, such. for example, as distance type thermometersutilize a Bourdon tube to actuate an indicator in response to thevariations of pressure produced by the expansion and contraction of anexpansive liquid in a remotely located bulb.

In order to obtain a wide, open, uniform scale and accurate anddependable readings, it has been found necessary to eliminate as manyparts which might contribute errors as by lost motion-as possible. Thishas resulted in the use of a longer pressure responsive element whichhas been wound into such forms as a double helix having inner and outercoils or a spiral coil. These forms of pressure responsive element haveparts at different diameters. Inasmuch as the flexibility of the Bourdontube is a function of the radius of curvature, it is not uniformthroughout the length of the coil. I have found that this lack ofuniformity is quite appreciable and that it results in compelling theouter coils to assume more than their share of the distortion due topressure changes. The inner coils, on account of the stiffness inherentin the smaller diameter of coil. operate at a much reduced efficiency.

The present invention contemplates the provision of a pressureresponsive element wherein the coil is provided with stiffening means inthe parts of larger radius so that the inner parts may be rendered moreefficient; for the intended purpose. The invention also contemplates toprovide the stiffening member in any desired part of the coil.

Other objects of the invention include the provision of a method formaking tubes hav ing the characteristics above outlined.

In the accompanying drawings two forms of the invention are illustratedin detail together with the method of forming up the element, it beingunderstood that the drawings are for purposes of illustrating theinvention, which is. not necessarily limited thereto. In these drawings:

Fig. 1 is a cross section of a flat piece of tubing suitable for makinginto a Bourdon tubef Fig. 2 shows a spiral coil made up in accordancewith the present invention;

Fig. 3 shows the end of the tubing shaped to form the outer part of thecoil;

Fig. 4 is a longitudinal section through 1924. Serial No. 726,231.

suitable dies showing the formation of the part shown in Fig. 3;

Fig. 5 is a cross section on the line 55 of Fig. 4; and

Fig. 6 illustrates a double helical coil to which the present inventionhas been applied.

In making up pressure responsive elements in accordance with the presentinvention one may utilize a flattened tube of the proper material andsize for the particular instrument in which the Bourdon tube is to beused. A cross-section of such a flattened tube is illustrated at 10 inFig. 1, where it will be noted that the flattened tube is openedslightly at 11 and 12,

It has heretofore been the practice to wind such flattened tubingdirectly into the coil, but the present invention contemplates anintermediate step which is illustrated in Figs. 4 and 5. One end of theflattened tubing is placed between a pair of cooperative dies 14 and 15one of which is provided with a longitudinal depression 16 which isopposite a longitudinal rib 17 on the other die. \Vhen pressure isapplied to the dies, a longitudinal rib is produced in the end portionof the strip of flattened tubing. Such a ridge is shown at 18. Where thestrip of tubing is to be used in making a spiral coil (such as shown inFig. 2) I prefer to gradually taper the depression 16 and rib 17 in thedies, as more clearly shown in Fig. 4, so as to produce a taperinglongitudinal rib or ridge along the tubing.

The proper length oftubing is then wound into a coil 20 of thepredetermined diameter. Such a coil is illustrated in Fig. 2. Here theouter end 21 of the coil is mounted in a fixed support 22 while theinner end 23 is adapted for connection with an indicating hand, notshown. The tapering ridge or rib 18 extends from the support around theouter convolutions of the coil, thereby rendering these convolutionssomewhat more rigid than the inner ones. lVhen the ribs is made taperingthe rigidity of the convolutions varies inversely with the distance fromthe outer or supported end of the complete coil.

I have found thatcoils made up as above described provide a very openand uniform scale, and that all parts of the coil may be made tofunction in the intended manner by varying the stiffness by means of therib or ridge which is formed into the tubing before it is wound into thecoil.

If desired, one may provide the dies 14 and 15 with opposed depressions24 and 25 and, in conjunction with other dies (not shown), form enlargedopenings 26 and 27 which are adapted to receive the pressure tubing 28and the sealing tube 29.

Fig. 6 shows a double helical coil form of pressure responsive element30. In making up such a coil according to the present invention, oneprovides the length of strip which is to go into the outer convolutionsill with a long ridge or rib 32 which extends from the end convolution33 down to the other end 34 of the coil where it is suitably supportedin the instrument. The end convolution is spirally wound and has adecreasing diameter to reach to the inner convolutions 35. Thisconvolution is preferably provided with a rib 36 of varying height sothat there will be a gradual variation in the rigidity of thisconvolution as its radius of curvature changes, In this form of coil onemay, however, omit the tapering feature in the end coil 33 and rely uponthe dill'erence in rigidity in the inner and outer coils which would beproduced by uniform ridge or rib 32.

It is obvious that the invention may be practiced with reference to manyforms and constructions, and I wish it to be understood that theparticular forms shown are but a few of the many forms. Variousmodifications and changes being possible, I do not limit myself in anyway with respect thereto.

\Vhat I claim is:

1. ABourdon tube having a plurality of coils of different diameter andmeans for rendering the outer coils stiffer than the inner coils.

2. A coiled Bourdon tube having a plurality of convolutions, the outerconvolutions having a stiffening rib arranged to render the outerconvolutions stifi'er than the inner convolutions.

3. A coiled Bourdon tube having a plurality of convolutions, the outerconvolutions having a stiffening rib, the height of the rib varyinginversely as the distance from the outer end of the coil.

4. A Bourdon coil having a reinforcement of gradually diminishingrigidity toward the center of the coil.

5. In a pressure responsive element, a fixed support, a Bourdon tubewhose outer end is mounted in the support and whose inner end is free,said tube having a plurality of coils of different diameter and meansfor rendering the outer coils stiffer than the inner coils.

6. In a pressure responsive element, a fixed support, a Bourdon tubewhose outer end is mounted in the support and whose inner end is free,said tube having a plurality of coils of different diameter and a rib ofdecreasing height to render the outer coils progressively stilier thanthe inner coils.

7. A Bourdon tube having the outer coils thereof progressively stiffenedby a stitfening rib of non-uniform cross section.

8. A coiled Bourdon tube of small cross section throughout its length,having coils of varying diameter, the stiffness of the coils varyingsubstantially as their diameter.

9. A sensitive element for instruments, comprising an elongated elasticmember, of small substantially uniform cross section. area throughoutits length wound into coil shape and shaped to have a graduallydiminishing degree of rigidity from the outer end toward the inner end.

10. A Bourdon coil of substantially uniform cross section for use inpressure sensitive instruments, designed to flex in response topressure, said coil having different degrees of rigidity at diflerentportions of its length, the rigidity of the various portions beingproportioned to the flexing forces set up simultaneously at suchportions by a change of pressure.

In testimony whereof'I have afiixed my signature to this specification.

H. SCHLAICH.

